The Effects of Xylazine Administration on Peripheral Leukocyte Values in Thoroughbred Horses

This study was conducted to determine whether xylazine administration is associated with clinically significant changes on leukocyte numbers in horses, as has been previously reported in other species. The study was designed to detect 20% changes in primary endpoint leukocyte parameters with 85% statistical power. No clinically significant changes in leukocyte numbers meeting the requirements of the statistical analysis were detected; no consistent changes capable of confounding a clinical diagnosis or treatment were detected. No gross changes in secondary endpoints including erythrocyte and platelet numbers were observed. No sensitivities associated with gender or age in either primary leukocyte or secondary erythrocyte, and platelet endpoints were detected graphically. All pre- and post-treatment leukocyte, erythrocyte, and platelet values remained within or very near normal ranges. It was concluded that a clinical dose of 0.5 mg/kg xylazine can be used in healthy horses without generating spurious changes in clinical hematology numbers that could confound clinical diagnoses or treatment.